Structural, optical and light sensing properties of carbon-ZnO films prepared by pulsed laser deposition

Abstract

There has been tremendous interest in ZnO as well as carbon materials; these are already in various technological devices. Work on the combination of ZnO and carbon materials is gaining interest [8-10] since these composites benefit from the good properties of both popular materials. For instance, carbon modified ZnO materials have been presented for solar cells and sensors to name a few. In light sensing, single carbon nanotubes mixed with ZnO have been employed. The current voltage characteristics obtained on the SWNTs –ZnO devices were found to be non-rectifying and Ohmiclike in the dark and when exposed to optical radiation. While the conductivity of SWNTs thin films was observed to increase by 7 % under UV illumination, similarly tested SWNT-ZnO samples consistently exhibited a decrease in conductivity upon exposure to UV radiation yielding a net negative change of 10 % associated with the formation of ZnO-SWNT interface. This effect as well as that of strong optical gating was explained within the model of interface mediated charging/discharging effects. In the present study, the aim was to push the UV and visible light sensing efficiency of the multi-wall carbon- nanotube-modified ZnO (MWCNT-ZnO) to higher values than 10 % by developing MWCNT-ZnO materials at varying processing temperatures from 300 K to 1173 K. This ensures that for the same starting MWCNTZnO composite, the proportions of MWCNT/ZnO are tuned by the process temperatures. In this work, the structural, morphological and optical properties of MWCNT-ZnO processed at varying temperatures are reported and how the process temperature impinges on structure, surface roughness and optical band gap energy of the MWCNT-ZnO composites calculated from reflectivity as well as the UV and visible light sensing of these composites is also discussed. It is demonstrated the light sensing efficiency can be pushed to above 50 %.